The formation of lens fibers is accompanied by an induction of yield-crystallin synthesis and definitive morphological changes. A thorough knowledge of normal lens development is essential for an understanding of the causes of cogenital cataracts and other pathological conditions of lens ontongeny such as aphakia. Despite the fact that the neural retina is known in a variety of systems to secrete factors which promote lens fiber formation, no such factor has been identified in a mammal. Isolation of such a factor would provide a powerful tool with which to study the regulation of lens fiber formation. We propose to develop a model in vitro assay system for this activity using central lens epithelial explants from mice. We will use both biochemical and immunological techniques to determine if the cells have been induced to synthesize yield-crystallin and light and electron microscopy to confirm if the morphological changes which accompany fiber formation have occurred. This system will then be exploited to detect the presence of and subsequently isolate such factors from mammalian vitreous and from serum-free media conditioned by a human retinoblastoma continuous cell line (Y-79). We believe that the fact that Y-79 secretes growth factors for lens epithelial cells in culture and the presumptive neural retinal stem cell origin of retinoblastoma indicate that these cells are secreting factors that are involved in promoting lens fiber formation. We also propose to determine if viral (Rubella) and chemical (corticosteroids) agents that have been associated with cataractogenesis in vivo can in any way effect the lens fiber promoting activity of factors in the vitreous or modulate the pattern of protein synthesis in our model system. We will also establish explants from mice with hereditary cataracts (e.g., Nakano) and determine if the competency to respond to lens fiber promoting agents and the pattern of protein synthesis is in any way different than that of normal mice of the same age. We will then determine if the factors we isolate function in vivo by using immunocytochemical techniques to establish if they are present in normal and cataractous lens' and by determining if antibodies to these factors can perturb lens development when introduced in utero.